Types of dielectrics used in semiconductor manufacturing include oxides, nitrides, borophosphosilicate glasses (BPSG), silicon-dioxides, silicon-nitrides, and tetra-ethyl-ortho-silicates (TEOS). During an integrated circuit manufacturing process, these dielectrics are often etched. For example, insulating oxides are etched, protective oxides are etched, and sacrificial oxide masks are etched. Dielectrics sometimes function as insulators to isolate one level of conductors and devices from another. However, the conductors and devices on different levels must be interconnected in order to have a working integrated circuit. This is accomplished by etching holes in the dielectric layers in order to connect one layer to another. In the art of integrated circuit manufacturing, these etched holes are referred to as contacts or vias. In this document, all holes etched in a dielectric are referred to simply as contacts.
A long standing problem in the art of manufacturing integrated circuits is that of completing a process step and not knowing whether the process step completed successfully. If the step did not complete successfully, and the processing of the integrated circuit continues, then it is likely that at the end of the manufacturing process the circuit will not work as designed. Thus, continued processing after a failed process step results in wasting the costs of processing after the failed step.
In the etching of dielectrics, a problem that can cause a processing step to fail is the failure of the process to completely etch the dielectric at a contact location. This failure prevents devices from being connected. One approach to solving this problem is to design the etching process to over etch, i.e., to run the process longer than necessary for etching some contacts in order to completely etch all contacts on the substrate. One difficulty with this approach is that over etching results in some contacts being etched to dimensions larger than necessary, and this interferes with the important goal of integrated circuit manufacturing of increasing the density of the devices on a substrate.
For these and other reasons, there is a need for the present invention.